Frinx coding challenges

Hello, you curious mind!

We see you've found our coding challenges. Feel free to solve any (or all) of them. Then, create a pull request with your solutions. We will review it and if it passes our tests, we would be thrilled to invite you for a formal interview.

Who knows? Maybe you're the next member of our team.

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Here are the challenges for Python:
(All of these should be solved without importing any libraries.)

1. Write a function that returns a list of indices of capital letters in a string. For example, given string "PYthOn", the function should return [0,1,4].

2. Write a recursive function that checks whether a string is a palindrome. A palindrome is a word that reads the same backward or forward. Therefore, given input strings "tenet" or "redder", your function should return True. Given strings "frinx" and "python", it should return False.

3. Write a function that transposes a matrix. In python, you can represent this matrix
   
   as a nested list:
   [[1,2,3], [4,5,6], [7,8,9]]
   After succesfully implementing the transposition, your function should return
   [[1,4,7], [2,5,8], [3,6,9]]
   Extra points: Perform the tranposition in one line of code.

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